WASHINGTON - Scientists are watching an iceberg bigger than the island of Guam as it slowly moves away from an Antarctic glacier.

NASA scientist Kelly Brunt said it is more a wonder than a worry and is not a threat to shipping or sea level rise.

Brunt said the iceberg, named B-31, is about 255 square miles (660 million sq. kilometers), roughly six times as big as Manhattan and as much as 1,600 feet (487 meters) thick. It broke off from the critical Pine Island Glacier last fall and researchers have been watching it move away ever since.

She said it is completely natural for icebergs to split off from glaciers in Antarctica, however this calving does shrink the Pine Island Glacier beyond its 30-year normal.